Star Trek IV: The Voyage Home

Spock is alive and well, only Earth might not be so lucky. As the Kirk, Bones, Scotty, and the rest of Enterprise Crew prepare to return to Earth to face charges for stealing a starship to rescue Spock, an vast alien intelligence attacks the planet for unknown reason. As the Enterprise crew returns to Earth, Spock decodes the signal the alien is sending down to Earth's oceans. Turns out that the alien is trying to contact whales, which are extinct in the 23rd century. So to save the Earth, and the rest of the Federation, Kirk, Spock, Bones, and the rest of the crew must travel back in time in a renegade Klingon spaceship to 20th century Earth in order to obtain a breeding pair of whales to communicate with the alien intelligence.